Cathode grid assembly



Jan. 15, 1952 POHLE 2,582,454

CATHODE GRID ASSEMBLY Filed May 15, 1950 2 SHEETSSHEET l INVENTOR. ERIC POHLE ATTOREYS Jan. 15, 1952 POHLE 2,582,454

CATHODE GRID ASSEMBLY Filed May 13, 1950 2 SHEETS-SHEET 2 29 & Fig. 7

INVENTOR. ERIC POP/LE ATTOREYS Patented Jan. 15, 1952 2,582,454 I C E CATHODE GRID ASSEMBLY Eric Pohle, Clifton, N. J., assignor to Allen B. Du Mont Laboratories, Inc., Clifton, N. J., a

corporation of Delaware Application May 13, 1950, Serial No. 161,793

Claims. 1

This invention relates to electron discharge devices and particularly to the electron gun portion of cathode raytubes, and more particularly to the cathode grid assembly of said tubes.

In the manufacture of cathode grid assemblies for cathode ray tubes, a mechanical spacer has been used to fix the distance between the electron emissive coating on the cathode and the grid aperture. Since the distance to be controlled is of the order of .005 inch. a tolerance of requires that these spacers vary in size no more than +.O005 inch. It is diflicult to obtain pressed or drawn metal spacers havin the required accuracy and a large percent age must be rejected. Furthermore, since the error is not entirely confined to the spacer but may be the result of incorrect stamping of other elements of the structure, it frequently happens that the complete cathode grid assembly is constructed before it is found to be outside of the tolerances thereb increasing the expense of the rejected part.

Other cathode grid assemblies which have been made without the use of mechanical spacers to determine the spacing between the cathode and grid, have been subject to a tilting of the axis of the cathode with respect to the grid. This cannot be controlled because of the inaccessibility of the cathode and cannot be determined until the cathode ray tube is completed and tested.

Consequently one object of my invention is to provide an improved cathode grid assembly.

A second object is to provide a cathode grid assembly, for a cathode ray tube, which can be rapidly and accurately assembled.

Other objects will be apparent from the specification and drawings in which:

Figure l is an isometric view of a cathode grid assembly;

Figure 2 shows a bottom view of the cathode grid assembly in Figure 1;

Figure 3 is a cross sectional view through 3-3 of the device in Figure 2;

Figure 4 shows a cathode thimble in its holder;

Figure 5 is a bottom View of the device in Figure 4;

Figure 6 illustrates apparatus used in one method of assembly of a cathode grid assembly; and

Figure 7 is a bottom view of one part of the device shown in Figure 6.

The invention will be described with reference to Figure 3, in which a cathode ray tube grid cylinder II is shown. made in accordance with known principles. One end of the cylinder II is capped by a disc l2 having a ring l3 on the rim thereof clasped by the matching rib I4 on the cylinder The disc I2 has a central aperture I6 and a stiffening rib H.

The cathode comprises a cap IS on which the emitting material I9 is located and a sleeve 20 inserted in and preferably welded to the cap I8 to form the complete cathode structure. This structure is mounted in the centrally located hole of a ceramic disc 2| and is held in place by the flange 22 of cap I8 on one side and by a bead 23 pressed into the cylinder 20 on the other side of the disc 2|.

Figures 4 and 5 show the disc 2| held in a metallic rim 24 by means of a plurality of fingers 2B which are cut from the cylindrical side of the rim 24. The openings 25 in the disc 2| assist in the evacuation of the cathode grid structure durin the final construction of the cathode ray tube. The rim 24 has a slot 21 therein for a purpose to be hereinafter explained.

Figure 6 shows a cathode grid similar to the one in Figure 3 in position for sealing the rim 24 to the grid cylinder The reference characters Ill and H2 indicate that the parts so designated are electrically equivalent to parts designated II and I2 in Figure 3. They differ mechanically in that the cylinder Ill and the disc ||2 are integrally formed from a single piece of metal. The two types of grid cylinders H and III are interchangeable for welding.

A microscope 3| mounted on a stand, which may be part of a vise 28, moved vertically by means of a knob 32, may be used to locate accurately the cathode with respect to the anode. In assembling the cathode grid structure, the vise 28 is opened as shown in Figure 7, which is a bottom view, and the cylinder III is slipped in place. The cylinder IN is locked in place with the disc H2 against the shoulder 33 of the vise 28. Space 34 is provided for the rim M if a structure such as that shown in Figure 3 is used.

If a one piece grid cylinder Ill and disc H2 is used, the focus of the microscope 3| can be fixed on a point which is below the top surface of the disc M2 by a distance equal to the thickness of the disc I I2 plus .005 inch, or the desired spacing. If a grid structure such as is shown in Figure 3 is used, the stiffening ring forms the abutting surface for the disc I2 against the shoulder 33. Since the height of the rib I! may vary, it is necessary first to focus the microscope 3| on the top surface of the disc |2 adjacent the aperture l6 and then refocus on a second point the required distance below the first point. Any of a number of well known gauging techniques may be used to determine the relation between the first and second focussing points.

Having fixed the microscope 3| at the second focussing point, the cathode assembly is then inserted into the grid cylinder A mounting device 29, mounted on guides (not shown) which allow it to slide coaxially into the cylinder may be used to insert the cathode assembly into the position where the emissive material I9 is at the second focussing point. The device 29 has a central pole 34, which fits snugly into the oathode cylinder 20 to keep it from tilting with respect to the grid cylinder and arms 36, which may be in the form of an open ended cylinder.

The arms 36 form the abutting surfaces since they rest on the comparatively sturdy insulating disc 2 I, while the central pole serves as the guide.

When the cathode assembly is properly positioned within the grid cylinder III, the welding electrodes 31 and 38 spot weld the rim 24 to the cylinder III to complete the construction of the cathode grid assembly.

The purpose of the slot 21 in the rim 24 (Figs. 4 and 5) is to allow the rim 24 to be made with a slightly larger external diameter than the internal diameter of the cylinder II I. This results in some friction, which is desirable, when the cathode assembly is inserted in the cylinder III. This friction, if not excessive, aids in positioning the cathode assembly properly within the cylinder III by resisting relative movement between the rim 24 and the cylinder I I I, thus holding the disc 2| tightly against the arms 36. Standard manufacturing tolerances for the cylinder III and rim 24 make this slot feature desirable.

. An alternative way of welding the rim 24 to the control grid cylinder I II is to utilize the arms, or outer cylinder 36 as. the inner electrodes in place of the electrodes 33. In order to do this it will be, of course, necessary to increase the outer diameter of the cylinder 36 to conform with the inner diameter of the skirt portion of the rim 24. The fingers 26, instead of the ceramic 2|, will then rest on top of the arms 36, but since the center aligning rod 34 maintains the alignment of the cathode, the assembly will not be misaligned.

A third way of welding the rim 24 to the cylinder I II is to utilize only the welding electrodes 31 in which case the mounting device 29 need not even be constructed of conducting material. This last mentioned type of welding consists in applying one polarity of the welding potential to one of the electrodes 31 and the other polarity to the other electrode 31. Welding then takes place at the areas of contact of the rim 24 and the cylinder III closest to the two electrodes 31.

Although I have illustrated this invention by specific examples of cathode grid assemblies and manufacturing devices, obvious alternatives will occur to those skilled in the art, and therefore I do not desire to be limited except by the following claims.

What is claimed is:

l. A cathode grid assembly for a cathode ray tube, said assembly comprising a cathode in the form of a cylinder closed at one end with the outer surface of said closed end being coated with an electron emissive material, a grid in the form of a cylinder closed at one end and having a central aperture in said closed end, said cathode being mounted coaxially within said grid with the closed ends in the same longitudinal direction and supported therein by an insulating disc secured thereto, and a mounting rim around the outer edge of said disc pressing against the inner surface of the sides of said grid preventing relative longitudinal movement between said cathode and said grid.

2. A cathode grid assembly for a cathode ray tube said assembly comprising a cathode comprising a hollow tube open at one end and closed at the other end by a heat conducting cover, said cover having a coating of electron emissive material on the surface thereof which is external to said tube and perpendicular to the axis of said tube, an insulating disc to which said tube is secured, a metallic rim around the perimeter of said disc, an inturned flange on said rim to restrict said disc from moving axially with respect to said rim in one direction, and projections from said rim to restrict said disc from moving axially with respect to said rim in the opposite direction, a control electrode comprising a hollow cylinder closed at one end in the form of a flat, apertured plate, said rim being secured coaxially within said cylinder and positioned to locate the closed end of said cathode nearest said apertured plate and the open end of said cathode tube nearest the open end of said cylinder.

3. A cathode grid assembly for a cathode ray tube said assembly comprising a cathode cornprising a hollow tube open at one end and closed at the other end by a heat conducting cover, said cover having a coating of electron emissive material on the surface thereof which is external to said tube and perpendicular to the axis of said tube, an insulating disc to which said tube is secured, a metallic rim around the perimeter of said disc, an inturned flange on said rim to restrict said disc from moving axially with respect to said rim in one direction, projections from said rim to restrict said disc from moving axially with respect to said rim in the opposite direction, a control electrode comprising a hollow cylinder and a fiat, apertured plate on one end of said cylinder, said rim being welded inside said cylinder and coaxially therewith and positioned to locate the closed end of said cathode nearest said apertured plate and the open end of said cathode ray nearest the open end of said cylinder.

4. The apparatus of claim 3 in which said rim has a longitudinal slot forming an opening to create resiliency of said rim.

5. A cathode grid assembly for a cathode ray tube said assembly comprising a cathode comprising a hollow tube open at one end and closed at the other end by a heat conducting cover, said cover having a coating of electron emissive material on the surface thereof which is external to said tube and perpendicular to the axis of said tube, an insulating disc to which said tube is secured, a metallic rim around the perimeter of said disc, an inturned flange on said rim to restrict said disc from moving axially with respect to said rim in the opposite direction, a control electrode comprising two semi-cylindrical sections joined along the sides thereof to form a hollow cylinder, and a fiat, apertured plate attached to one end of said cylinder, said rim being welded inside said cylinder and coaxially therewith and positioned to locate the closed end of said cathode nearest said apertured plate and the open end of said cathode tube nearest the open end of said cylinder.

ERIC POHLE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,705,356 Bohner Mar. 29, 1920 2,244,358 Ewald June 3, 1941 2,393,057 OLarte et al Jan. 15, 1946 2,431,137 OLarte et a1 Nov. 18, 1947 2,432,789 OLarte et al Dec. 16, 1947 2,436,265 Pohle Feb. 17, 1948 2,443,916 Kelar June 22, 1948 2,459,532 Ickis Jan. 18, 1949 2,476,060 Moss July 12, 1949 2,507,979 Kelar May 16, 1950 2,510,267 Tolson June 6, 1950 

